Fix csp mode on platforms that don't support __proto__.

tests/language/mixin_proto_test.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Tests that a program in csp mode doesn't access the prototype chain
+// on platforms that don't support direct access to __proto__.
+// This test is most useful with --csp and on a platform that doesn't support
+// __proto__ access (such as Rhino).
+// See http://dartbug.com/27290 .
+
+import 'package:expect/expect.dart';
+
+class A {
+  var x;
+  foo() => 44;
+  bar() => 22;
+}
+
+class B {
+  var y;
+  foo() => 42;
+}
+
+class C extends A with B {
+  var z;
+  bar() => 499;
+}
+
+main() {
+  var all = [new A(), new B(), new C()];

[sra1, 2017/02/23 23:43:39]

Always use a 'confuse' function to obfuscate.
It would take only a couple of tweaks to type inference to be able to inline the
calls.

[floitsch, 2017/02/24 12:35:29]

https://codereview.chromium.org/2712603006/

+  Expect.equals(44, all[0].foo());
+  Expect.equals(22, all[0].bar());
+  Expect.equals(42, all[1].foo());
+  Expect.equals(42, all[2].foo());
+  Expect.equals(499, all[2].bar());
+}